Income Taxes - Components of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024
Deferred tax assets:
Accrued expenses not currently deductible	$ 256.7	$ 237.4
Stock-based compensation expense	56.0	51.3
Foreign tax credits	8.8	12.0
Fixed and intangible assets	216.8	194.9
Net operating losses	59.3	41.7
Disallowed business interest expense carryforward	30.9	0.0
Unrealized investment losses, net	98.4	351.4
Other	28.5	39.1
Deferred tax assets, gross	755.4	927.8
Less: valuation allowances	(23.8)	(11.1)
Deferred tax assets, net	731.6	916.7
Deferred tax liabilities:
Deferred contract costs	654.0	620.7
Prepaid expenses	103.1	88.8
Prepaid retirement benefits	53.1	40.3
Tax on unrepatriated earnings	12.0	10.2
Other	16.9	20.8
Deferred tax liabilities	839.1	780.8
Net deferred tax (liabilities)/assets	$ (107.5)
Net deferred tax (liabilities)/assets		$ 135.9